Damper and vehicle seat equipped with the damper

ABSTRACT

A damper includes a vessel for accommodating a viscous fluid in its interior; hampering walls for hampering the flow of the viscous fluid; a partitioning member which partitions each of interior portions into two chambers and is provided rotatably; a communicating hole formed in the partitioning member so as to allow the two chambers to communicate with each other via a variable passage whose passage cross-sectional area changes; a flow limiter to limit the flow of the viscous fluid in the chamber into the chamber through the communicating hole, when the internal pressure of the viscous fluid accommodated in the chamber has exceeded a fixed value on the basis of the rotation of the partitioning member; and a resilient structure to resiliently urge the partitioning member in a direction with respect to the vessel.

This application is a divisional of U.S. application Ser. No.12/989,748, filed on Dec. 1, 2010, now allowed, which is the U.S.National Phase of International Application No. PCT/JP2009/001806, filedon Apr. 20, 2009, which designated the U.S. and claims priority toJapanese Application No. 2008-117912, filed on Apr. 28, 2008, the entirecontents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a damper for absorbing an impact, andmore particular to a damper suitable for use in a vehicle seat having aheadrest for supporting the head of a seated person by moving forwardwhen, at the time of such as a collision of a motor vehicle, the seatedperson moves backward due to inertia upon receiving an impact from therear, as well as a vehicle seat equipped with the damper.

BACKGROUND ART

-   Patent Document 1: JP-A-10-181403-   Patent Document 2: JP-A-10-119619-   Patent Document 3: JP-A-11-268566-   Patent Document 4: JP-A-2003-81044-   Patent Document 5: JP-A-2003-176844-   Patent Document 6: JP-A-2005-225334-   Patent Document 7: JP-A-2006-82772-   Patent Document 8: JP-A-2006-88875

In motor vehicles, vehicle seats have been proposed in which a headrestis adapted to move forward to restrict the head of a seated person atthe time of such as a collision.

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

Incidentally, shock absorbing dampers which are used in such vehicleseats are required to be such that, in the collision at the time of lowspeed, the impact caused by the collision is absorbed softly in order tosupport the head so as not to impart the impact, whereas, in thecollision at the time of high speed, the impact is absorbed withstiffness corresponding to the magnitude of the impact at the time ofthe collision so as to absorb the impact due to the collision bybecoming stiff in order to support the head reliably.

The present invention has been devised in view of the above-describedaspects, and its object is to provide a damper capable of softlyabsorbing an impact when the impact is small, and of becoming stiff andpositively holding an impact-absorbed body, e.g., the head, when theimpact is large.

Another object of the invention is to provide a vehicle seat which iscapable of positively moving the headrest in the forward direction onlyat the time of such as a collision by properly discriminating the timeof such as a collision and the time of a non-collision, and which can becompactly installed in a backrest and the like.

Means for Solving the Problems

The damper in accordance with the present invention comprises: a vesselfor accommodating a viscous fluid in its interior; at least onehampering wall provided in the interior of the vessel to hamper the flowof the viscous fluid in a direction about an axis of the vessel; apartitioning member for partitioning the interior of the vesselaccommodating the viscous fluid whose flow has been hampered by thehampering wall into at least two chambers in the direction about theaxis, the partitioning member being provided in the interior of thevessel rotatably in the direction about the axis with respect to thevessel; at least one communicating hole formed in the partitioningmember so as to allow the two chambers in the interior of the vessel tocommunicate with each other via a variable passage whose passagecross-sectional area changes; and flow limiting means for limiting theflow of the viscous fluid in the chamber on one direction side in thedirection about the axis into the chamber on another direction side inthe direction about the axis through the communicating hole when theinternal pressure of the viscous fluid accommodated in the chamber onthe one direction side in the direction about the axis has exceeded afixed value on the basis of the rotation of the partitioning member inthe one direction in the direction about the axis with respect to thevessel, wherein the flow limiting means includes: a variable passageforming member which has a through hole which, in an end face in the onedirection in the direction about the axis of the variable passageforming member, is open to the chamber on the one direction side in thedirection about the axis, the variable passage forming member beingfitted to the partitioning member movably in such a manner as to oppose,at an end face in another direction in the direction about the axis ofthe variable passage forming member, a side face in the one direction inthe direction about the axis of the partitioning member, so as to formthe variable passage communicating with, on one side, the through holeand, on another side, the communicating hole in cooperation with theside face in the one direction in the direction about the axis of thepartitioning member; and an annular elastic member surrounding thevariable passage and disposed between the end face in the otherdirection in the direction about the axis of the variable passageforming member and the side face in the one direction in the directionabout the axis of the partitioning member, so as to brake the relativerotation in the direction about the axis of the partitioning member withrespect to the vessel.

According to the above-described damper, in the case of the input ofrelative rotation of the partitioning member with respect to the vesselat a low velocity not exceeding a fixed value, the partitioning memberis rotated with respect to the vessel in one direction in the directionabout the axis at a low velocity not exceeding the fixed value, and theinternal pressure of the viscous fluid accommodated in the chamber onthe one direction side in the direction about the axis of the vesseldoes not exceed a fixed value. Therefore, the annular elastic memberdisposed between the end face in the other direction in the directionabout the axis of the variable passage forming member and the side facein the one direction in the direction about the axis of the partitioningmember is not greatly deformed elastically, and a large passage crosssection of the variable passage is maintained. Thus, the viscous fluidaccommodated in the chamber on the one direction side in the directionabout the axis is allowed to flow into the chamber on the otherdirection side through the through hole, the variable passage, and thecommunicating hole without much resistance. As a result, a resultantdamping force, i.e., a reaction force with respect to the input ofrotation, is set to a relatively small value based on the flowresistance in the case where the viscous fluid flows through the throughhole, the variable passage, and the communicating hole. On the otherhand, in the case of the input of high-speed relative rotation of thepartitioning member with respect to the vessel in excess of the fixedvalue, the partitioning member tends to be rotated with respect to thevessel in the one direction in the direction about the axis at a highvelocity exceeding the fixed value, and the internal pressure of theviscous fluid accommodated in the chamber on the one direction side inthe direction about the axis of the vessel exceeds a fixed value.Therefore, the annular elastic member sandwiched between the end face inthe other direction in the direction about the axis of the variablepassage forming member and the side face in the one direction in thedirection about the axis of the partitioning member is deformedelastically. Hence, the distance in the direction about the axis betweenthe end face in the other direction in the direction about the axis ofthe variable passage forming member and the side face in the onedirection in the direction about the axis of the partitioning memberbecomes small, so that the passage cross section of the variable passagebecomes small. Thus, large resistance occurs in the flow of the viscousfluid accommodated in the chamber on the one direction side in thedirection about the axis of the vessel into the chamber on the otherdirection side in the direction about the axis of the vessel through thethrough hole, the variable passage, and the communicating hole. As aresult, a resultant damping force, i.e., a reaction force with respectto the input of rotation, assumes a magnitude which is based on thecompression resistance of the viscous fluid in the chamber on the onedirection side in the direction about the axis and the flow resistanceof the viscous fluid through the variable passage having the passagecross section which has become small. Thus, in the case of the input oflow-speed rotation not exceeding a fixed value in which case the impactis small, the impact is absorbed softly, whereas in the case of theinput of high-speed rotation exceeding the fixed value in which case theimpact is large, the damper becomes stiff so as to be able to positivelyhold the impact-absorbed body. Hence, the relative rotation in thedirection about the axis of the partitioning member with respect to thevessel can be braked satisfactorily.

In the damper in a preferred example, the variable passage formingmember has a plate-like portion having the through hole, a leg portionformed, at its one end portion, integrally on the plate-like portion andinserted in the communicating hole, and a hook portion formed integrallyon another end portion of the leg portion so as to prevent the legportion from coming off the communicating hole. Further, thepartitioning member has a truncated conical surface in the side face inthe one direction in the direction about the axis, the variable passageforming member has a truncated conical surface which is complementary tothe truncated conical surface of the partitioning member and opposesthat truncated conical surface, and the variable passage has a truncatedconical passage formed by the truncated conical surface of thepartitioning member and the truncated conical surface of the variablepassage forming member.

The damper in accordance with the present invention comprises: a vesselfor accommodating a viscous fluid in its interior; at least onehampering wall provided in the interior of the vessel to hamper the flowof the viscous fluid in a direction about an axis of the vessel; apartitioning member for partitioning the interior of the vesselaccommodating the viscous fluid whose flow has been hampered by thehampering wall into at least two chambers in the direction about theaxis, the partitioning member being provided in the interior of thevessel rotatably in the direction about the axis with respect to thevessel; at least one communicating hole formed in the partitioningmember so as to allow the two chambers in the interior of the vessel tocommunicate with each other via a variable passage whose passagecross-sectional area changes; and flow limiting means for limiting theflow of the viscous fluid in the chamber on one direction side in thedirection about the axis into the chamber on another direction side inthe direction about the axis through the communicating hole when theinternal pressure of the viscous fluid accommodated in the chamber onthe one direction side in the direction about the axis has exceeded afixed value on the basis of the rotation of the partitioning member inthe one direction in the direction about the axis with respect to thevessel, wherein the flow limiting means includes: a variable passageforming member which is movably fitted to the partitioning member andhas, in its end face in the other direction in the direction about theaxis facing a side face in the one direction in the direction about theaxis of the partitioning member, a communicating groove which is open atits one end portion to the chamber on the one direction side in thedirection about the axis and is open at its other end portion to thecommunicating hole; and an annular elastic member which is locatedbetween the one end portion and the other end portion of thecommunicating groove in a radial direction and fitted to the side facein the one direction in the direction about the axis of the partitioningmember, such that the variable passage for effecting mutualcommunication between the two chambers in the vessel by means of thecommunicating hole by allowing the chamber on the one direction side inthe direction about the axis and the communicating hole to communicateis formed by the contact, pressing contact, and non-contact of theannular elastic member with respect to the end face in the otherdirection in the direction about the axis of the variable passageforming member having the communicating groove, so as to brake therelative rotation in the direction about the axis of the partitioningmember with respect to the vessel.

According to the above-described damper, in the case of the input ofrelative rotation of the partitioning member with respect to the vesselat a low velocity not exceeding a fixed value, the partitioning memberis rotated with respect to the vessel in one direction in the directionabout the axis at a low velocity not exceeding the fixed value, and theinternal pressure of the viscous fluid accommodated in the chamber onthe one direction side in the direction about the axis of the vesseldoes not exceed a fixed value. Therefore, the annular elastic memberfitted at the side face in the one direction in the direction about theaxis of the partitioning member is not strongly brought into pressingcontact and is not greatly deformed elastically by the end face in theother direction in the direction about the axis of the variable passageforming member, with the result that a large passage cross-sectionalarea is maintained for the variable passage. Thus, the viscous fluidaccommodated in the chamber on the one direction side in the directionabout the axis is allowed to flow into the chamber on the otherdirection side in the direction about the axis through the variablepassage and the communicating hole without much resistance. As a result,a resultant damping force, i.e., a reaction force with respect to theinput of rotation, is set to a relatively small value based on the flowresistance in the case where the viscous fluid flows through thevariable passage having a large passage cross-sectional area and thecommunicating hole. On the other hand, in the case of the input ofhigh-speed relative rotation of the partitioning member with respect tothe vessel in excess of the fixed value, the partitioning member tendsto be moved with respect to the vessel in the one direction in thedirection about the axis at a high velocity exceeding the fixed value,and the internal pressure of the viscous fluid accommodated in thechamber on the one direction side in the direction about the axis of thevessel exceeds a fixed value. Therefore, the annular elastic memberlocated between the end face in the other direction in the directionabout the axis of the variable passage forming member and the side facein the one direction in the direction about the axis of the partitioningmember is brought into contact with the end face in the other directionin the direction about the axis of the variable passage forming member,so that the variable passage is constituted only by the communicatinggroove, thereby rendering the passage cross-sectional area of thevariable passage small. Further, as the end face in the other directionin the direction about the axis of the variable passage forming memberafter the contact is further pressed and contacted against the annularelastic member, the annular elastic member is greatly deformedelastically. As the annular elastic member is embedded into thecommunicating groove by this large elastic deformation of the annularelastic member, the passage cross-sectional area of the variable passagebecomes even smaller. Thus, large resistance occurs in the flow of theviscous fluid accommodated in the chamber on the one direction side inthe direction about the axis of the vessel into the chamber on the otherdirection side in the direction about the axis of the vessel through thevariable passage and the communicating hole. As a result, a resultantdamping force, i.e., a reaction force with respect to the input ofrotation, assumes a magnitude which is based on the compressionresistance of the viscous fluid in the chamber on the one direction sidein the direction about the axis and the flow resistance of the viscousfluid through the variable passage having the passage cross-sectionalarea which has become small. Thus, in the case of the input of low-speedrotation not exceeding a fixed value in which case the impact is small,the impact is absorbed softly, whereas in the case of the input ofhigh-speed rotation exceeding the fixed value in which case the impactis large, the damper becomes stiff so as to be able to positively holdthe impact-absorbed body. Hence, the relative rotation in the directionabout the axis of the partitioning member with respect to the vessel canbe braked satisfactorily.

In the above-described damper in another preferred example, the variablepassage forming member has a plate-like portion having the communicatinggroove, a leg portion formed, at its one end portion, integrally on theplate-like portion and inserted in the communicating hole, and a hookportion formed integrally on another end portion of the leg portion soas to prevent the leg portion from coming off the communicating hole.Further, when the internal pressure of the viscous fluid accommodated inthe chamber in the other direction in the direction about the axis isgenerated in excess of a fixed value on the basis of the rotation of thepartitioning member in the other direction in the direction about theaxis with respect to the vessel, the end face in the other direction inthe direction about the axis of the variable passage forming member isadapted to move away from the annular elastic member. Furthermore, whenthe internal pressure of the viscous fluid accommodated in the chamberon the one direction side in the direction about the axis is generatedin excess of a fixed value on the basis of the rotation of thepartitioning member in the one direction in the direction about the axiswith respect to the vessel, the annular elastic member is adapted to beelastically deformed to fill the communicating groove and reduce thepassage cross-sectional area of the variable passage.

The above-described damper which is adapted to brake the relativerotation in the direction about the axis of the partitioning member withrespect to the vessel may further comprise resilient means forresiliently urging the partitioning member in the other direction in thedirection about the axis with respect to the vessel.

Still another damper in accordance with the present invention comprises:a vessel for accommodating a viscous fluid in its interior; apartitioning member provided in the interior of the vessel linearlymovably in an axial direction with respect to the vessel to partitionthe interior of the vessel for accommodating the viscous fluid into atleast two chambers in the axial direction; at least one communicatinghole formed in the partitioning member so as to allow the two chambersin the interior of the vessel to communicate with each other through avariable passage whose passage cross-sectional area changes; flowlimiting means for limiting the flow of the viscous fluid in the chamberon one direction side in the axial direction into the chamber on anotherdirection side in the axial direction through the communicating holewhen the internal pressure of the viscous fluid accommodated in thechamber on the one direction side in the axial direction has exceeded afixed value on the basis of the linear movement of the partitioningmember in one direction in the axial direction with respect to thevessel, wherein the flow limiting means includes: a variable passageforming member which has a through hole which, in an end face in the onedirection in the axial direction of the variable passage forming member,is open to the chamber on the one direction side in the axial direction,the variable passage forming member being fitted to the partitioningmember movably in such a manner as to oppose, at an end face in anotherdirection in the axial direction of the variable passage forming member,a side face in the one direction in the axial direction of thepartitioning member, so as to form the variable passage communicatingwith, on one side, the through hole and, on another side, thecommunicating hole in cooperation with the side face in the onedirection in the axial direction of the partitioning member; and anannular elastic member surrounding the variable passage and disposedbetween the end face in the other direction in the axial direction ofthe variable passage forming member and the side face in the onedirection in the axial direction of the partitioning member, so as tobrake the relative linear movement in the axial direction of thepartitioning member with respect to the vessel.

According to the above-described damper, in the case of the input ofrelative linear motion of the partitioning member with respect to thevessel at a low velocity not exceeding a fixed value, the partitioningmember is linearly moved with respect to the vessel in one direction inthe axial direction at a low velocity not exceeding the fixed value, andthe internal pressure of the viscous fluid accommodated in the chamberon the one direction side in the axial direction of the vessel does notexceed a fixed value. Therefore, the annular elastic member disposedbetween the end face in the other direction in the axial direction ofthe variable passage forming member and the side face in the onedirection in the axial direction of the partitioning member is notgreatly deformed elastically, and a large passage cross section of thevariable passage is maintained. Thus, the viscous fluid accommodated inthe chamber on the one direction side in the axial direction is allowedto flow into the chamber on the other direction side through the throughhole, the variable passage, and the communicating hole without muchresistance. As a result, a resultant damping force, i.e., a reactionforce with respect to the input of linear motion, is set to a relativelysmall value based on the flow resistance in the case where the viscousfluid flows through the through hole, the variable passage, and thecommunicating hole. On the other hand, in the case of the input ofhigh-speed relative linear motion of the partitioning member withrespect to the vessel in excess of the fixed value, the partitioningmember tends to be moved linearly with respect to the vessel in the onedirection in the axial direction at a high velocity exceeding the fixedvalue, and the internal pressure of the viscous fluid accommodated inthe chamber on the one direction side in the axial direction of thevessel exceeds a fixed value. Therefore, the annular elastic membersandwiched between the end face in the other direction in the axialdirection of the variable passage forming member and the side face inthe one direction in the axial direction of the partitioning member isdeformed elastically. Hence, the distance in the axial direction betweenthe end face in the other direction in the axial direction of thevariable passage forming member and the side face in the one directionin the axial direction of the partitioning member becomes small, so thatthe passage cross section of the variable passage becomes small. Thus,large resistance occurs in the flow of the viscous fluid accommodated inthe chamber on the one direction side in the axial direction of thevessel into the chamber on the other direction side in the axialdirection of the vessel through the through hole, the variable passage,and the communicating hole. As a result, a resultant damping force,i.e., a reaction force with respect to the input of linear motion,assumes a magnitude which is based on the compression resistance of theviscous fluid in the chamber on the one direction side in the axialdirection and the flow resistance of the viscous fluid through thevariable passage having the passage cross section which has becomesmall. Thus, in the case of the input of low-speed linear motion notexceeding a fixed value in which case the impact is small, the impact isabsorbed softly, whereas in the case of the input of high-speed linearmotion exceeding the fixed value in which case the impact is large, thedamper becomes stiff so as to be able to positively hold theimpact-absorbed body. Hence, the relative rotation in the axialdirection of the partitioning member with respect to the vessel can bebraked satisfactorily.

In still another preferred example of the above-described damper, thevariable passage forming member has a plate-like portion having thethrough hole, a leg portion formed, at its one end portion, integrallyon the plate-like portion and inserted in the communicating hole, and ahook portion formed integrally on another end portion of the leg portionso as to prevent the leg portion from coming off the communicating hole.Further, the partitioning member has a truncated conical surface in theside face in the one direction in the axial direction, the variablepassage forming member has a truncated conical surface which iscomplementary to the truncated conical surface of the partitioningmember and opposes that truncated conical surface, and the variablepassage has a truncated conical passage formed by the truncated conicalsurface of the partitioning member and the truncated conical surface ofthe variable passage forming member.

A further damper in accordance with the present invention comprises: avessel for accommodating a viscous fluid in its interior; a partitioningmember provided in the interior of the vessel linearly movably in anaxial direction with respect to the vessel to partition the interior ofthe vessel for accommodating the viscous fluid into at least twochambers in the axial direction; at least one communicating hole formedin the partitioning member so as to allow the two chambers in theinterior of the vessel to communicate with each other through a variablepassage whose passage cross-sectional area changes; flow limiting meansfor limiting the flow of the viscous fluid in the chamber on onedirection side in the axial direction into the chamber on anotherdirection side in the axial direction through the communicating holewhen the internal pressure of the viscous fluid accommodated in thechamber on the one direction side in the axial direction has exceeded afixed value on the basis of the linear movement of the partitioningmember in one direction in the axial direction with respect to thevessel, wherein the flow limiting means includes: a variable passageforming member which is movably fitted to the partitioning member andhas, in its end face in another direction in the axial direction facinga side face in the one direction in the axial direction of thepartitioning member, a communicating groove which is open at its one endportion to the chamber on the one direction side in the axial directionand is open at its other end portion to the communicating hole; and anannular elastic member which is located between the one end portion andthe other end portion of the communicating groove in a radial directionand fitted to the side face in the one direction in the axial directionof the partitioning member, such that the variable passage for effectingmutual communication between the two chambers in the vessel by means ofthe communicating hole by allowing the chamber on the one direction sidein the axial direction and the communicating hole to communicate isformed by the contact, pressing contact, and non-contact of the annularelastic member with respect to the end face in the other direction inthe axial direction of the variable passage forming member having thecommunicating groove, so as to brake the relative linear movement in theaxial direction of the partitioning member with respect to the vessel.

According to the above-described damper, in the case of the input ofrelative linear motion of the partitioning member with respect to thevessel at a low velocity not exceeding a fixed value, the partitioningmember is linearly moved with respect to the vessel in one direction inthe axial direction at a low velocity not exceeding the fixed value, andthe internal pressure of the viscous fluid accommodated in the chamberon the one direction side in the axial direction of the vessel does notexceed a fixed value. Therefore, the annular elastic member fitted atthe side face in the one direction in the axial direction of thepartitioning member is not greatly deformed elastically by the end facein the other direction in the axial direction of the variable passageforming member, with the result that a large passage cross-sectionalarea is maintained for the variable passage. Thus, the viscous fluidaccommodated in the chamber on the one direction side in the axialdirection is allowed to flow into the chamber on the other directionside in the axial direction through the variable passage and thecommunicating hole without much resistance. As a result, a resultantdamping force, i.e., a reaction force with respect to the input oflinear motion, is set to a relatively small value based on the flowresistance in the case where the viscous fluid flows through thevariable passage having a large passage cross-sectional area and thecommunicating hole. On the other hand, in the case of the input ofhigh-speed relative linear motion of the partitioning member withrespect to the vessel in excess of the fixed value, the partitioningmember tends to be moved with respect to the vessel in the one directionin the axial direction at a high velocity exceeding the fixed value, andthe internal pressure of the viscous fluid accommodated in the chamberon the one direction side in the axial direction of the vessel exceeds afixed value. Therefore, the annular elastic member located between theend face in the other direction in the axial direction of the variablepassage forming member and the side face in the one direction in theaxial direction of the partitioning member is brought into contact withthe end face in the other direction in the axial direction of thevariable passage forming member, so that the variable passage isconstituted only by the communicating groove, thereby rendering thepassage cross-sectional area of the variable passage small. Further, asthe end face in the other direction in the axial direction of thevariable passage forming member after the contact is further pressed andcontacted against the annular elastic member, the annular elastic memberis not strongly brought into pressing contact and is greatly deformedelastically. As the annular elastic member is embedded into thecommunicating groove by this large elastic deformation of the annularelastic member, the passage cross-sectional area of the variable passagebecomes even smaller. Thus, large resistance occurs in the flow of theviscous fluid accommodated in the chamber on the one direction side inthe axial direction of the vessel into the chamber on the otherdirection side in the axial direction of the vessel through the variablepassage and the communicating hole. As a result, a resultant dampingforce, i.e., a reaction force with respect to the input of linearmotion, assumes a magnitude which is based on the compression resistanceof the viscous fluid in the chamber on the one direction side in theaxial direction and the flow resistance of the viscous fluid through thevariable passage having the passage cross-sectional area which hasbecome small. Thus, in the case of the input of low-speed linear motionnot exceeding a fixed value in which case the impact is small, theimpact is absorbed softly, whereas in the case of the input ofhigh-speed linear motion exceeding the fixed value in which case theimpact is large, the damper becomes stiff so as to be able to positivelyhold the impact-absorbed body. Hence, the relative linear motion in theaxial direction of the partitioning member with respect to the vesselcan be braked satisfactorily.

According to a further preferred example of the damper, the variablepassage forming member has a plate-like portion having the communicatinggroove, a leg portion formed, at its one end portion, integrally on theplate-like portion and inserted in the communicating hole, and a hookportion formed integrally on another end portion of the leg portion soas to prevent the leg portion from coming off the communicating hole.Further, when the internal pressure of the viscous fluid accommodated inthe chamber in the other direction in the axial direction is generatedin excess of a fixed value on the basis of the linear movement of thepartitioning member in the other direction in the axial direction withrespect to the vessel, the end face in the other direction in the axialdirection of the variable passage forming member is adapted to move awayfrom the annular elastic member. Still further, when the internalpressure of the viscous fluid accommodated in the chamber on the onedirection side in the axial direction is generated in excess of a fixedvalue on the basis of the linear movement of the partitioning member inthe one direction in the axial direction with respect to the vessel, theannular elastic member is adapted to be elastically deformed to fill thecommunicating groove and reduce the passage cross-sectional area of thevariable passage.

The damper which is adapted to brake the relative linear motion in theaxial direction of the partitioning member with respect to the vesselmay also further comprise resilient means for resiliently urging thepartitioning member in the other direction in the axial direction withrespect to the vessel.

In any one of the above-described dampers, the annular elastic member ina preferred example is constituted by an O-ring formed of natural rubberor synthetic rubber whose modulus of elasticity is small at a hightemperature (the annular elastic member becomes soft) and large at a lowtemperature (the annular elastic member becomes hard). The annularelastic member formed such an O-ring undergoes large elastic deformationat high temperature and small elastic deformation at low temperature. Asa result, coupled with the synergistic action with the viscous fluidhaving a positive temperature characteristic concerning fluidity wherebythe fluidity increases at high temperature and the fluidity decreases atlow temperature, it is possible to reduce the temperature dependence ofthe flow resistance of the viscous fluid flowing through the variablepassage having a passage cross-sectional area determined by the elasticdeformation of the annular elastic member. Thus, it is possible toreduce the difference, for instance, between, on the one hand, thestiffness of the damper in the direction about the axis or in the axialdirection in the case of an input of high-speed rotation or linearmovement exceeding a fixed value in which case the impact becomes largeat high temperature and, on the other hand, the stiffness of the damperin the direction about the axis or in the axial direction in the case ofan input of high-speed rotation or linear movement exceeding the fixedvalue in which case the impact becomes large at low temperature. Hence,it becomes possible to positively hold the impact-absorbed body withstiffness which does not differ so much both at high temperature and atlow temperature with respect to the direction about the axis or theaxial direction. In the invention, the annular elastic member is notlimited to one constituted by an O-ring formed of natural rubber orsynthetic rubber, and may be formed of an elastic material such aspolyurethane rubber, acrylic rubber, silicone rubber, polyesterelastomer, or the like. Furthermore, the annular elastic member may beconstituted by a ring or the like whose cross-sectional shape is of asquare type, a Y-type, a U-type, a V-type, or an X-type.

As the viscous fluid used in the invention, silicone oil of 100 to 1000cst is suitable, but is not limited to the same.

Furthermore, a vehicle seat in accordance with the present inventioncomprises: a backrest of a vehicle; a headrest supported by the backrestmovably in a forward direction of the vehicle; movement urging means forurging the headrest to move in the forward direction; and an inhibitionmechanism for inhibiting the movement of the headrest in the forwarddirection; and canceling means for canceling the inhibition by theinhibition mechanism of the movement of the headrest in the forwarddirection when a moving velocity of a force applied to the backrest in abackward direction of the vehicle has exceeded a fixed value, thecanceling means having a load-rotation converting mechanism forconverting a load applied to a back receiving portion of the backrestinto a rotational force and a transmitting mechanism for transmitting tothe inhibition mechanism a force applied to the backrest in the backwarddirection of the vehicle on the basis of the moving velocity exceedingthe fixed value, the transmitting mechanism having the damper accordingto any one of claims 1 to 15, wherein one of the vessel and thepartitioning member of the damper is coupled to the load-rotationconverting mechanism, and another one of the vessel and the partitioningmember of the damper is coupled to the inhibition mechanism.

According to the vehicle seat in accordance with the above-describedaspect of the invention, the canceling means, which cancels theinhibition by the inhibition mechanism of the movement of the headrestin the forward direction when a moving velocity of a force applied tothe backrest in a backward direction of the vehicle has exceeded a fixedvalue, has a transmitting mechanism for transmitting to the inhibitionmechanism a force applied to the backrest in the backward direction ofthe vehicle on the basis of the moving velocity exceeding the fixedvalue. Moreover, since the transmitting mechanism has the damperaccording to any one of the above-described forms, it is possible topositively move the headrest in the forward direction only at the timeof such as a collision by properly discriminating the time of such as acollision and the time of a non-collision, and the damper and the likecan be compactly installed in the backrest and the like.

The load-rotation converting mechanism may have a load receiving platesupported rotatably by a frame of the backrest and disposed in the backreceiving portion of the backrest. Further, the headrest may besupported by the backrest rotatably or linearly movably in the forwarddirection, the movement urging means may be adapted to urge the headrestto rotate or linearly move in the forward direction, and the inhibitionmechanism may be adapted to inhibit the rotation or linear movement ofthe headrest in the forward direction.

Advantages of the Invention

According to the invention, it is possible to provide a damper capableof softly absorbing an impact when the impact is small, and of becomingstiff and positively holding an impact-absorbed body, e.g., the head,when the impact is large. In addition, it is possible to provide avehicle seat equipped with a damper which is capable of positivelymoving the headrest in the forward direction only at the time of such asa collision by properly discriminating the time of such as a collisionand the time of a non-collision, and in which the damper and the likecan be compactly installed in the backrest and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory cross-sectional view, taken in the direction ofarrows along line I-I shown in FIG. 3, of a preferred embodiment of theinvention;

FIG. 2 is an explanatory cross-sectional view, taken in the direction ofarrows along line II-II shown in FIG. 3, of the embodiment shown in FIG.1;

FIG. 3 is an explanatory cross-sectional view, taken in the direction ofarrows along line III-III, of the embodiment shown in FIG. 1;

FIG. 4 is an explanatory partial enlarged view of the embodiment shownin FIG. 1;

FIG. 5 is an explanatory exploded view of the embodiment shown in FIG.4;

FIG. 6( a) is an explanatory view taken in the direction of arrows alongline VIa-VIa shown in FIG. 5, and FIG. 6( b) is an explanatory viewtaken in the direction of arrows along line VIb-VIb shown in FIG. 5,both in the embodiment shown in FIG. 5;

FIG. 7 is a right side elevational view of a variable passage formingmember shown in FIG. 5;

FIG. 8 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIG. 9 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIG. 10 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIG. 11 is an explanatory side elevational view of an embodiment inwhich the embodiment shown in FIG. 1 is used in a vehicle seat;

FIG. 12 is an explanatory front elevational view of the embodiment shownin FIG. 11;

FIG. 13 is an explanatory partial diagram of another preferredembodiment of the invention;

FIG. 14 is an explanatory exploded view of a portion shown in FIG. 13;

FIG. 15 is an explanatory enlarged view of the variable passage formingmember shown in FIG. 13;

FIG. 16 is a right side elevational view of the variable passage formingmember shown in FIG. 15;

FIG. 17( a) is an explanatory view taken in the direction of arrowsalong line XVIIa-XVIIa shown in FIG. 14, and FIG. 17( b) is anexplanatory view taken in the direction of arrows along line XVIIb-XVIIbshown in FIG. 14, both in the embodiment shown in FIG. 14;

FIG. 18 is a diagram explaining the operation of the embodiment shown inFIG. 18;

FIG. 19 is a diagram explaining the operation of the embodiment shown inFIG. 18;

FIG. 20 is an explanatory diagram of still another preferred embodimentof the invention;

FIG. 21 is a diagram explaining the operation of the embodiment shown inFIG. 20;

FIG. 22 is an explanatory side elevational view of an embodiment inwhich the embodiment shown in FIG. 20 is used in a vehicle seat; and

FIG. 23 is an explanatory front elevational view of the embodiment shownin FIG. 22.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, a more detailed description will be given of the presentinvention and the mode for carrying it out with reference to thepreferred embodiments shown in the drawings. It should be noted that thepresent invention is not limited to these embodiments.

In FIGS. 1 to 7, a damper 1 in accordance with this embodiment iscomprised of a vessel 4 for accommodating a viscous fluid 3 in itsinterior 2 and having an axis O; at least one hampering wall, in thisembodiment two hampering walls 5 and 6, which are provided in theinterior 2 of the vessel 4 to hamper the flow of the viscous fluid 3 inan R1 direction and an R2 direction which are one and the otherdirection in a direction R about the axis O of the vessel 4; apartitioning member 11 whereby each of interior portions 7 and 8 splitinto two concerning the R1 and R2 directions by the hampering walls 5and 6 in the interior 2 of the vessel 4 accommodating the viscous fluid3 whose flow has been hampered by the hampering walls 5 and 6 ispartitioned into two chambers 9 and 10 in the R1 and R2 directions, thepartitioning member 11 being provided in the interior 2 of the vessel 4rotatably in the R1 and R2 directions with respect to that vessel 4; acommunicating hole 13 formed in the partitioning member 11 so as toallow the two chambers 9 and 10 in the interior 2 of the vessel 4 tocommunicate with each other via a variable passage 12 whose passagecross-sectional area changes; a flow limiting means 14 for limiting theflow of the viscous fluid 3 in the chamber 9 on the R1 direction sideinto the chamber 10 on the R2 direction side, which is the otherdirection in the direction about the axis O, through the communicatinghole 13, when the internal pressure of the viscous fluid 3 accommodatedin the chamber 9 on the R1 direction side has exceeded a fixed value onthe basis of the rotation of the partitioning member 11 in the R1direction, which is one direction in the direction about the axis O,with respect to the vessel 4; and a resilient means 15 for resilientlyurging the partitioning member 11 in the R2 direction with respect tothe vessel 4.

The vessel 4 includes a hollow cylindrical portion 21; a bottom portion22 which is integrally provided at one end in an A1 direction, i.e., onedirection in an axial direction A, of the hollow cylindrical portion 21,and which closes the open plane in the A1 direction of the hollowcylindrical portion 21; an outer peripheral collar portion 23 which isintegrally provided at one end in an A2 direction, i.e., the otherdirection in the direction about the axis A; and an annular closuremember 25 which is secured to the collar portion 23 by rivets or screws24 and closes the open plane in the A2 direction of the hollowcylindrical portion 21.

The hollow cylindrical portion 21 has an annular notch 28 formed at anannular end face 26 in the A2 direction so as to accommodate a seal ring27 constituted by an O-ring. The bottom portion 22 includes adisk-shaped body 29 formed integrally on the hollow cylindrical portion21; a shaft portion 31 formed integrally on the body 29 in such a manneras to project from a central portion of a side face 30 in the A2direction of the body 29 into the interior 2 in the A2 direction; and abottomed hole 33 which is provided in a central portion of the body 29and a central portion of the shaft portion 31 and into which a supportshaft, a connecting member or the like is inserted from an opening of aside face 32 in the A1 direction of the body 29 and is fitted therein.The closure member 25 integrally has an annular body 34, a hollowcylindrical portion 36 projecting in the A1 direction from an innerperipheral side of a side face 35 in the A1 direction of the body 34,and a hollow cylindrical portion 37 projecting in the A1 direction froman outer peripheral side of the side face 35 in the A1 direction of thebody 34, the closure member 25 being secured to the collar portion 23 bythe rivets or screws 24 at outer peripheral side portions of the body 34and the hollow cylindrical portion 37. The seal ring 27 fitted in thenotch 28 is pressed by an annular end face 38 in the A1 direction of thehollow cylindrical portion 37.

The hampering walls 5 and 6, which are integrally formed on acylindrical inner peripheral surface 41 of the hollow cylindricalportion 21 in such a manner as to project from that inner peripheralsurface 41 toward the axis O, extend in the direction about the axis A,and oppose each other in the radial direction, respectively have slidingend faces 42 and 43 on their radially inner sides. The hampering wallsare not limited to the two hampering walls which are arranged at anequiangular interval of 180° in the direction R as in this embodiment,and the number thereof may be one, or three or more which are arrangedpreferably at equiangular intervals in the direction R.

The partitioning member 11 includes a columnar main body 45 which ispassed through the closure member 25; two blade portions 47 and 48 whichare integrally formed on a cylindrical outer peripheral surface 46 ofthe main body 45 in such a manner as to project from that outerperipheral surface 46 in the radially outward direction, extend in thedirection about the axis A, and oppose each other in the radialdirection symmetrically about the axis O; a collar portion 49 which isintegrally formed on the main body 45 and the blade portions 47 and 48disposed in the interior 2; and a hollow cylindrical portion 51 which isintegrally formed on a side face 50 in the A2 direction of the collarportion 49 and extends in such a manner as to project from that sideface 50 in the A2 direction, and which has a greater diameter than thehollow cylindrical portion 36 and surrounds the hollow cylindricalportion 36.

The main body 45 has a cylindrical bottomed hole 56 which is bored in anend face 55 in the A1 direction and is adapted to rotatably receive theshaft portion 31, as well as a bottomed hole 59 which is bored in an endface 57 in the A2 direction and into which a rotating shaft 58 is fittedand mounted. The outer peripheral surface 46 of the main body 45 is inliquid-tight contact with the sliding end faces 42 and 43 on theradially inner sides of the hampering walls 5 and 6 slidably in the R1and R2 directions. Each of sliding end faces 61 and 62 on respectiveradially outer sides of the blade portions 47 and 48 is in liquid-tightcontact with the inner peripheral surface 41 of the hollow cylindricalportion 21 slidably in the R1 and R2 directions. A seal ring 63 isdisposed between the hollow cylindrical portion 51 and the hollowcylindrical portion 36.

The partitioning member 11 which thus integrally has the main body 45,the blade portions 47 and 48, the collar portion 49, and the hollowcylindrical portion 51 is supported at its main body 45 by the closuremember 25 and the shaft portion 31 rotatably in the R1 and R2directions, and is relatively rotatable in the R1 and R2 directions withrespect to the vessel 4. Hence, as the rotating shaft 58 fitted in thebottomed hole 59 is rotated in the R1 and R2 directions, thepartitioning member 11 is adapted to be rotated in the same directions.

In this embodiment, the interior 2 is partitioned into two interiorportions 7 and 8 in the direction R about the axis by the two hamperingwalls 5 and 6, and each of the interior portions 7 and 8 is partitionedinto the two chambers 9 and 10 in the R1 and R2 directions by the bladeportions 47 and 48 respectively disposed in the interior portions 7 and8. However, in a case where the flow in the R1 direction and the R2direction of the viscous fluid 3 in the interior 2 is hampered by onehampering wall, the interior 2 may be partitioned into the two chambers9 and 10 by one blade portion, or the interior 2 may be partitioned intothree or more chambers by a plurality of blade portions. Still further,the interior 2 may be partitioned into two or more interior portionswhere the flow of the viscous fluid 3 in the R1 direction and the R2direction is hampered by two or more hampering walls, and two or moreblade portions may be disposed in each of the interior portions thuspartitioned into two or more so as to partition each of these interiorportions into three or more chambers.

Since the blade portion 47 side and the blade portion 48 side areconstructed identically in this embodiment, the blade portion 47 sidewill hereafter be described in detail, and the blade portion 48 sidewill be described as required.

The blade portion 47 has a plate-like body 65 which has the sliding endface 61 at its radially outer free end and is formed integrally on themain body 45 at its radially inner end. As shown in particular detail inFIGS. 4 to 6, the blade portion 47 further includes, in addition to theplate-like body 65, a disk-shaped portion 67 projecting integrally froma side face 66 in the R1 direction of the plate-like body 65; atruncated conical portion 70 projecting in the R1 direction integrallyfrom an end face 68 in the R1 direction of the disk-shaped portion 67and having a truncated conical surface 69; a columnar projection 71projecting integrally from a projecting end in the R1 direction of thetruncated conical portion 70; a pair of through holes 72 penetrating theplate-like body 65 and the disk-shaped portion 67 and opposing eachother in the radial direction; and a circular hole 74 which communicatesat one end thereof with the through holes 72 and communicates at theother end thereof, i.e., at a side face 73 in the R2 direction of theplate-like body 65, with the chamber 10 and is open thereat. Thus, thepartitioning member 11, i.e., the blade portion 47, has on its sidefaces 75 in the R1 direction the side face 66, the end face 68, and thetruncated conical surface 69, and the communicating hole 13 of thepartitioning member 11 is constituted by the pair of through holes 72and the circular hole 74.

As shown in particular detail in FIGS. 4 to 7, the flow limiting means14, which is adapted to brake the relative rotation in the R directionof the partitioning member 11 with respect to the vessel 4, includes avariable passage forming member 85 which has a through hole 82 which, inan end face 81 in the R1 direction, is open to the chamber 9 on the R1direction side, the variable passage forming member 85 being fitted tothe blade portion 47 movably with respect to the blade portion 47 insuch a manner as to oppose, at its end face 84 in the R2 direction, theside face 66, the end face 68, and the truncated conical surface 69among the side faces 75 in the R1 direction of the blade portion 47, soas to form the variable passage 12 communicating with, on the one side,the through hole 82 and, on the other side, the pair of through holes 72of the communicating hole 13 in cooperation with the end face 68 and thetruncated conical surface 69 among the side faces 75 in the R1 directionof the blade portion 47; and an annular elastic member 86 constituted byan O-ring or the like and surrounding the disk-shaped portion 67 and thevariable passage 12, the annular elastic member 86 being disposedbetween the end face 84 in the R2 direction of the variable passageforming member 85 and the side face 75 in the R1 direction of the bladeportion 47.

The variable passage forming member 85 has a circular plate-like portion91 having the through hole 82 with the columnar projection 71 disposedtherein; a pair of leg portions 92 formed, at their one ends, integrallyon the plate-like portion 91 and respectively inserted in the throughholes 72; and hook portions 94 which are respectively formed integrallyon other end portions of the leg portions 92 projecting from the otherends of the through holes 72 and are engaged, at the other ends of thethrough holes 72, with an annular stepped surface 93 of the bladeportion 47, so as to prevent the leg portions 92 from coming off thethrough holes 72.

The end face 84 has an annular flat surface 100 with which one ends ofthe leg portions 92 are integrally formed and which are brought intocontact with the end face 68 and the annular elastic member 86 radiallyoutwardly of the leg portions 92; and a truncated conical surface 101which is surrounded by the flat surface 100, is complementary to thetruncated conical surface 69 of the partitioning member 11, opposes thattruncated conical surface 69, and is brought into contact with thetruncated conical surface 69.

The variable passage 12 has a truncated conical passage 105 formed bythe truncated conical surface 69 of the partitioning member 11 and thetruncated conical surface 101 of the variable passage forming member 85;an inner annular passage 106 communicating with the truncated conicalpassage 105 and formed by the end face 68 of the partitioning member 11and the flat surface 100 of the variable passage forming member 85radially inwardly of the leg portion 92; and an outer annular passage107 (see FIG. 10) communicating with the inner annular passage 106 andformed by the end face 68 of the partitioning member 11 and the flatsurface 100 of the variable passage forming member 85 radially outwardlyof the leg portions 92. The truncated conical passage 105 communicateswith the chamber 9 through an annular gap between the columnarprojection 71 disposed in the through hole 82 and the plate-like portion91 in that through hole 82, and the inner annular passage 106communicates with the pair of through holes 72 of the communicating hole13, while the outer annular passage 107 at its radially outer edgecommunicates with the chamber 9 when the contact of the flat surface 100with the annular elastic member 86 is canceled, as shown in FIG. 10.

The annular elastic member 86 is constituted by an O-ring formed ofnatural rubber or synthetic rubber whose modulus of elasticity is smallat a high temperature (the annular elastic member becomes soft) andlarge at a low temperature (the annular elastic member becomes hard).The annular elastic member 86 at its side face 108 in the R2 directionis in contact with the side face 66, and the annular elastic member 86at its inner peripheral surface 109 on the radially inner side iselastically fitted to a cylindrical outer peripheral surface 110 on theradially outer side of the disk-shaped portion 67, the annular elasticmember 86 being disposed in such a manner as to partially project fromthe end face 68 in the R1 direction.

The resilient means 15 has a spring (spiral spring) 111 in which anelongated plate having one end secured and connected on the outer sideof the vessel 4 to the annular body 34 of the closure member 25 and theother end secured and connected to the main body 45 of the partitioningmember 11 is wound in coil form. The arrangement provided is such thatthe partitioning member 11 is rotated in the R2 direction by theresiliency of the spiral spring 111 to thereby return to its initialposition.

In the slow, low-speed rotation in the R1 direction of the partitioningmember 11 in which the internal pressure of the viscous fluid 3 in thechamber 9 is not very large relative to the internal pressure of theviscous fluid 3 in the chamber 10, i.e., in the input of relativelow-speed rotation in the R1 direction from the rotating shaft 58against the resiliency of the spiral spring 111, the flow limiting means14 causes the flat surface 100 to be brought into pressing contact withthe annular elastic member 86 in contact with the side face 66, to suchan extent that the annular elastic member 86 is not greatly deformedelastically in its cross section diameter by the internal pressure ofthe viscous fluid 3 in the chamber 9, as shown in FIG. 4, to therebyblock the outer annular passage 107 and hamper the communication of thechamber 9 with the chamber 10 through the outer annular passage 107.Meanwhile, the chamber 9 is communicated with the chamber 10 through thetruncated conical passage 105 and the inner annular passage 106 eachhaving a passage cross section determined by the cross section diameterof the annular elastic member 86 which is not greatly deformedelastically in its cross section diameter, as well as through theannular gap between the columnar projection 71 and the plate-likeportion 91 in the through hole 82 and through the communicating holes13. A small resisting force is thus generated for the slow rotation ofthe partitioning member 11 in the R1 direction by allowing the flow ofthe viscous fluid 3 from the chamber 9 into the chamber 10 by theabove-described communication, as shown in FIG. 8.

In the high-speed rotation in the R1 direction of the partitioningmember 11 in which the internal pressure of the viscous fluid 3 in thechamber 9 becomes extremely large relative to the internal pressure ofthe viscous fluid 3 in the chamber 10, i.e., in the input of relativehigh-speed rotation in the R1 direction from the rotating shaft 58, theflow limiting means 14 causes the plate-like portion 91 of the variablepassage forming member 85 to move toward the annular elastic member 86by the large internal pressure of the chamber 9, and causes theplate-like portion 91 to be pressed against the annular elastic member86 so as to allow the annular elastic member 86 to be greatly deformedelastically in its cross section diameter owing to this movement,thereby narrowing the passage cross-sectional areas of the truncatedconical passage 105 and the inner annular passage 106. The chamber 9 ishence communicated with the chamber 10 through the truncated conicalpassage 105 and the inner annular passage 106 with their passagecross-sectional areas thus reduced. A large resisting force is thusgenerated for the high-speed rotation of the partitioning member 11 inthe R1 direction by causing the flow of the viscous fluid 3 from thechamber 9 into the chamber 10 with large resistance owing to theabove-described communication. Furthermore, in the rotation in the R1direction of the partitioning member 11 due to the input of relativerotation at an even higher speed in the R1 direction from the rotatingshaft 58, the annular elastic member 86 in its cross section diameter iseven more greatly crush-pressed and deformed elastically by the elasticcrush-pressing of the annular elastic member 86 by the plate-likeportion 91 of the variable passage forming member 85. Hence, thetruncated conical surface 101 is brought into contact with the truncatedconical surface 69, thereby closing the truncated conical passage 105.At the same time, the passage cross-sectional area of the inner annularpassage 106 is set to a minimal value, thereby substantially minimizingthe flow of the viscous fluid 3 in the chamber 9 into the chamber 10 andsubstantially stopping the above-described high-speed rotation throughthe partitioning member 11. Hence, the rotation of the impact-absorbedbody which tends to rotate the rotating shaft 58 at high speed isstopped, thereby making it possible to positively hold theimpact-absorbed body.

When the input of relative rotation in the R2 direction from therotating shaft 58 ceases, in the flow limiting means 14, thepartitioning member 11 begins to be conversely rotated relatively in theR2 direction by the resiliency of the spiral spring 111. In thisrotation, the variable passage forming member 85 is relatively moved inthe moving-away direction with respect to the partitioning member 11, asshown in FIG. 10. As a result, the outer annular passage 107 is reopenedto recover the communication between the chamber 9 and the communicatinghole 13 through the outer annular passage 107, and the truncated conicalpassage 105 and the inner annular passage 106 each having a largepassage cross section are formed, thereby causing the flow of theviscous fluid 3 from the chamber 9 into the chamber 10 with smallresistance. Hence, the partitioning member 11 is speedily rotated in theR2 direction with such a small resisting force, and the partitioningmember 11 is returned to its initial position in which the side face 73is brought into contact with the hampering wall 5.

The annular elastic member 86, which is made of natural rubber orsynthetic rubber having a small modulus of elasticity at hightemperature and a large modulus of elasticity at low temperature,undergoes large elastic deformation at high temperature and smallelastic deformation at low temperature in the crush-pressing by theplate-like portion 91. Therefore, coupled with the synergistic actionwith the viscous fluid 3 having a positive temperature characteristicconcerning fluidity whereby the fluidity increases at high temperatureand decreases at low temperature, it is possible to reduce thetemperature dependence of the flow resistance of the viscous fluid 3flowing through the variable passage 12 having a passage cross-sectionalarea determined by the elastic deformation of the annular elastic member86. Thus, it is possible to reduce the difference, for instance,between, on the one hand, the stiffness of the damper 1 in the R1direction in the case of an input of high-speed rotation exceeding afixed value in which case the impact becomes large at high temperatureand, on the other hand, the stiffness of the damper 1 in the R1direction in the case of an input of high-speed rotation exceeding thefixed value in which case the impact becomes large at low temperature.Hence, it becomes possible to positively hold the impact-absorbed bodywith stiffness which does not differ so much both at high temperatureand at low temperature with respect to the R1 direction.

The above-described damper 1, which is adapted to brake the relativerotation in the direction R about the axis O of the partitioning member11 with respect to the vessel 4, may be used for a vehicle seat 201, asshown in FIGS. 11 and 12. Namely, the vehicle seat 201 in accordancewith this embodiment is comprised of a seat 203 mounted on a floor 202of a vehicle such that its front-back position and inclined position areadjustable; a vehicle backrest 204 installed to the seat 203 such thatits inclined position is adjustable; a headrest 205 supported by thebackrest 204 movably in the forward direction, i.e., rotatably in aforward R3 direction in this embodiment; a rotatively urging means 206for rotatively urging the headrest 205 in the forward R3 direction; aninhibition mechanism 207 for inhibiting the rotation of the headrest 205in the R3 direction; and a canceling means 208 for canceling theinhibition by the inhibition mechanism 207 of the movement of theheadrest 205 in the R3 direction when the moving velocity of the forceapplied to the backrest 204 in the backward direction of the vehicle hasexceeded a fixed value.

Since the mechanism of mounting the seat 203 on the floor 202 such thatits front-back position and inclined position are adjustable and themechanism of installing the backrest 204 to the seat 203 such that itsinclined position is adjustable are publicly known, a detaileddescription thereof will be omitted.

The headrest 205 has a headrest body 211 and a supporting member 213which is secured to the headrest body 211 and is supported by a frame(not shown) of the backrest 204 rotatably in the R3 direction by meansof a shaft 212. The supporting member 213 is adapted to not rotate in anopposite direction to the R3 direction by a stopper 214 secured to theframe of the backrest 204.

The rotatively urging means 206 serving as a movement urging means has acoil spring 215 having one end secured to the frame of the backrest 204and the other end secured to the supporting member 213, so as toconstantly urge the headrest 205 rotatively in the R3 direction by theresiliency of the coil spring 215.

The inhibition mechanism 207 has a hook member 217 which is supported bya frame of the backrest 204 by means of a shaft 216 rotatably in an R4direction and abuts against and engages a leading end of the supportingmember 213 so as to inhibit the rotation of the supporting member 213 inthe R3 direction, as well as a stopper 218 and a coil spring 219 forsetting the hook member 217 to an abutting and engaging position withrespect to the leading end of the supporting member 213.

The canceling means 208 has a load-rotation converting mechanism 222which is displaced by the load applied to a back receiving portion 221of the backrest 204 from an occupant seated in the seat 203 and atransmitting mechanism 223 which transmits to the inhibition mechanism207 a force applied to the back receiving portion 221 of the backrest204 in the backward direction of the vehicle on the basis of itsvelocity exceeding a fixed value, but which does not transmit to theinhibition mechanism 207 the force applied to the back receiving portion221 of the backrest 204 on the basis of its velocity of the fixed valueor less.

The load-rotation converting mechanism 222 has the rotating shaft 58supported rotatably by the frame of the backrest 204 and a loadreceiving plate 225 secured to the rotating shaft 58 and disposed in theback receiving portion 221 of the backrest 204. The load receiving plate225 supported rotatably by the frame of the backrest 204 by means of therotating shaft 58 is embedded in a cushion in the back receiving portion221 of the backrest 204.

The transmitting mechanism 223 has a supporting shaft 226 supported bythe frame of the backrest 204, an arm member 227 supported by thesupporting shaft 226 rotatably in the R1 and R2 directions, the damper 1secured to the arm member 227, and a wire 228 having one end coupled tothe arm member 227 and the other end coupled to the hook member 217. Asfor the arm member 227, an unillustrated projection formed integrally onthat arm member 227 is secured to the damper 1 by being fitted in thebottomed hole 33 of the damper 1. Thus, the arm member 227, i.e., thevessel 4 of the damper 1, is supported by the frame of the backrest 204rotatably about the supporting shaft 226 in the R1 and R2 directions bymeans of the arm member 227. Meanwhile, the vessel 4 of the damper 1 issemi-fixed by the resiliency of the coil spring 219 by means of the wire228 and the hook member 217 with respect to the rotation in the R1direction.

In the above-described vehicle seat 201, in a case where the occupant isseated in the seat 203 and the occupant's normal load is applied to thebackrest 204 in the backward direction of the vehicle, or in a casewhere the occupant's load is added to the backrest 204 in the backwarddirection of the vehicle due to the normal acceleration of the vehiclefor the occupant seated in the seat 203, these loads upon the backrest204 are applied slowly at a velocity of a fixed value or less. As aresult, the load receiving plate 225 which receives such a load of theoccupant is rotated slowly about the rotating shaft 58 in the R1direction without causing the vessel 4, which is semi-fixed with respectto its rotation in the R1 direction by the resiliency of the coil spring219, to produce rotation in the R1 direction. This slow rotation of theload receiving plate 225 produces slow flow of the viscous fluid 3 fromthe chamber 9 into the chamber 10 through the truncated conical passage105 and the inner annular passage 106 each having a passage crosssection determined by the cross section diameter of the annular elasticmember 86 which is not greatly deformed elastically, and through theannular gap between the columnar projection 71 and the plate-likeportion 91 in the through hole 82, the through holes 72, and thecircular hole 74. In consequence, the load receiving plate 225 and,hence, the backrest 204 are subjected to a moderate impact. Meanwhile,in such slow rotation of the load receiving plate 225, the partitioningmember 11 is idled in the R1 direction with respect to the vessel 4, asshown in FIG. 8, so that the partitioning member 11 and the vessel 4 areset in an non-coupled state with respect to the rotation in the R1direction. As a result, a tensile force which produces the rotation inthe R4 direction of the hook member 217 such as to cancel the abutmentand engagement with the leading end of the supporting member 213 is notproduced in the wire 228 through the vessel 4. Thus, the inhibitionmechanism 207 inhibits the rotation of the headrest 205 in the forwardR3 direction, thereby maintaining the headrest 205 in its normalposition.

On the other hand, with the vehicle seat 201, when, upon a collisionfrom the rear, a large velocity in the backward direction exceeding afixed value has occurred in the occupant seated in the seat 203, and theload receiving plate 225 is suddenly rotated about the rotating shaft 58in the R1 direction, this rotation of the rotating shaft 58 in the R1direction at the velocity exceeding the fixed value limits the flow ofthe viscous fluid 3 from the chamber 9 into the chamber 10 by thetruncated conical passage 105 and the inner annular passage 106 eachhaving a passage cross section determined by the cross section diameterof the annular elastic member 86 which has been greatly deformedelastically. As a result, the vessel 4 and the partitioning member 11are set in a coupled state with respect to the rotation in the R1direction. In consequence, such rotation of the rotating shaft 58 in theR1 direction at a velocity exceeding the fixed value causes the vessel 4to undergo rotation about the supporting shaft 226 in the R1 directionthrough the partitioning member 11 against the resiliency of the coilspring 219. Thus, a tensile force producing the rotation of the hookmember 217 in the R4 direction so as to cancel the abutment andengagement with the leading end of the supporting member 213 is producedin the wire 228. Hence, the hook member 217 of the inhibition mechanism207 is rotated about the shaft 216 in the R4 direction so as to cancelthe abutment and engagement with the leading end of the supportingmember 213, with the result that the headrest 205 is rotated in the R3direction by being urged by the coil spring 215 so as to hold theoccupant's head.

Thus, the vehicle seat 201 has the transmitting mechanism 223 equippedwith the damper 1 serving as a switching mechanism whereby the forceapplied to the backrest 204 in the backward direction of the vehicle ata velocity exceeding a fixed value is transmitted to the inhibitionmechanism 207 so as to cancel the inhibition by the inhibition mechanism207 of the rotation of the headrest 205 in the forward R3 direction,whereas the force applied to the backrest 204 at a velocity of the fixedvalue or less is not transmitted to the inhibition mechanism 207 so asto maintain the inhibition by the inhibition mechanism 207 of therotation of the headrest 205 in the forward R3 direction. Therefore, itis possible to positively move the headrest 205 in the forward R3direction only at the time of such as a collision by properlydiscriminating the time of such as a collision and the time of anon-collision.

In the example of the above-described vehicle seat 201, the resetting ofthe abutment and engagement of the leading end of the supporting member213 with respect to the hook member 217 can be effected if, after themovement of the headrest 205 in the forward R3 direction, the headrest205 is forcibly rotated in the opposite direction to the R3 direction toallow the leading end of the supporting member 213 to slide on aninclined surface of the hook member 217 and to reversely rotate the hookmember 217. It should be noted that although the wire 228 is used in theabove-described embodiment, it is possible to alternatively use a gearmechanism, a rack and pinion mechanism, or the like.

In substitution of the above, an arrangement may be provided as shown inFIGS. 13 and 14. Namely, an annular projection 112 is formed integrallyon the side face 66 of the plate-like body 65 in such a manner as tosurround the disk-shaped portion 67 and concentrically with thedisk-shaped portion 67. The annular elastic member 86 is brought at itsside face 108 into contact with the side face 66, is elastically fittedat its inner peripheral surface 109 to the outer peripheral surface 110of the disk-shaped portion 67, and is disposed in an annular groove 113defined by the projection 112 and the disk-shaped portion 67 in such amanner as to partially protrude outside that annular groove 113.Further, one circular hole 115 defined by an annular inner peripheralsurface 114 of the disk-shaped portion 67 and the plate-like body 65 andcommunicating with the circular hole 74 is provided in the plate-likebody 65 of the blade portion 47. In this case, the communicating hole 13of the partitioning member 11 is constituted by the single circular hole115 and the circular hole 74.

Furthermore, a flow limiting means 116 shown in FIGS. 13 to 17 may beused in substitution of the above-described flow limiting means 14. Sucha flow limiting means 116 includes a variable passage forming member 122which is movably fitted to the plate-like body 65 of the partitioningmember 11 and has, in its end face 118 in the R2 direction facing theside face 66, a plurality of, i.e., in this embodiment two, radiallyextending communicating grooves 121 which are respectively open at theirone end portions 119 to the chamber 9 and are open at their other endportions 120 to the circular hole 115 of the communicating hole 13; andthe annular elastic member 86 which is located between the one endportion 119 and the other end portion 120 of each communicating groove121 in the radial direction and fitted to the side face 66 of theplate-like body 65 in the blade portion 47 of the partitioning member11, such that a variable passage 123 (see FIG. 19) including thecommunicating grooves 121 for effecting mutual communication between thetwo chambers 9 and 10 in the vessel 2 by means of the communicating hole13 by allowing the chamber 9 and the communicating hole 13 tocommunicate is formed by the contact, pressing contact, and non-contactof the annular elastic member 86 with respect to the end face 118 in theR2 direction of the variable passage forming member 122 having thecommunicating grooves 121.

The variable passage forming member 122 includes a circular plate-likeportion 125 having the end face 118 and the communicating grooves 121formed on the end face 118 symmetrically about the axis; a pair of legportions 126 which have respective one end portions formed integrally onthe plate-like portion 125, project from these one end portions, and areinserted in the circular hole 115 of the communicating hole 13; and hookportions 127 which are respectively formed integrally the other endportions of the pair of leg portions 126 and are engaged with theannular stepped surface 93 between the circular hole 115 and thecircular hole 74 so as to prevent the leg portions 126 from coming offthe circular hole 115 of the communicating hole 13.

As for the variable passage forming member 122 is fitted to the bladeportion 47 of the partitioning member 11 as its pair of leg portions 126at their outer peripheral surfaces 131 are movably brought into slidingcontact with the inner peripheral surface 114 of the plate-like body 65and the disk-shaped portion 67 defining the circular hole 115.

The variable passage 123 is constituted by an annular passage 133 whichis formed between the end face 118 of the plate-like portion 125 of thevariable passage forming member 122 and an annular outer peripheralsurface 132 of the annular elastic member 86, and whose passagecross-sectional area changes as the end face 118 of the plate-likeportion 125 approaches and moves away from that outer peripheral surface132; and the communicating grooves 121 whose passage cross-sectionalarea changes as a deforming portion of the annular elastic member 86 isembedded due to the elastic deformation of the annular elastic member 86by the pressing contact of the outer peripheral surface 132 with the endface 118 of the plate-like portion 125 and as the embedment is canceledon the basis of the cancellation of such pressing contact.

In the slow, low-speed rotation in the R1 direction of the partitioningmember 11 in which the internal pressure of the viscous fluid 3 in thechamber 9 is not very large relative to the internal pressure of theviscous fluid 3 in the chamber 10, i.e., in the input of relativelow-speed rotation in the R1 direction from the rotating shaft 58, theflow limiting means 116 causes the end face 118 of the variable passageforming member 122 to be brought into contact with the outer peripheralsurface 132 of the annular elastic member 86 to such an extent that theannular elastic member 86 is not greatly deformed elastically by theinternal pressure of the viscous fluid 3 in the chamber 9, as shown inFIG. 13, to thereby block the annular passage 133 and hamper thecommunication of the chamber 9 with the chamber 10 through the annularpassage 133. Meanwhile, the chamber 9 is communicated with the chamber10 through the communicating grooves 121 and the communicating hole 13.A small resisting force is thus generated for the slow rotation of thepartitioning member 11 in the R1 direction by allowing the flow of theviscous fluid 3 from the chamber 9 into the chamber 10 by theabove-described communication.

In the high-speed rotation in the R1 direction of the partitioningmember 11 in which the internal pressure of the viscous fluid 3 in thechamber 9 becomes extremely large relative to the internal pressure ofthe viscous fluid 3 in the chamber 10, i.e., in the input of relativehigh-speed rotation in the R1 direction from the rotating shaft 58, theflow limiting means 116 causes the annular elastic member 86 to begreatly deformed elastically in its cross section diameter owing to thepressing contact of the end face 118 of the variable passage formingmember 122 with respect to the outer peripheral surface 132 of theannular elastic member 86 by the large internal pressure of the chamber9, as shown in FIG. 18. As this resilient deformation causes thedeforming portion of the annular elastic member 86 to be embedded in thecommunicating grooves 121, the passage cross-sectional areas of thecommunicating grooves 121 are narrowed. The chamber 9 is hencecommunicated with the chamber 10 through the variable passage 123 withits passage cross-sectional area thus narrowed and through thecommunicating hole 13. A large resisting force is thus generated for thehigh-speed rotation of the partitioning member 11 in the R1 direction bycausing the flow of the viscous fluid 3 from the chamber 9 into thechamber 10 with large resistance owing to the above-describedcommunication. Furthermore, in the rotation in the R1 direction of thepartitioning member 11 due to the input of relative rotation at an evenhigher speed in the R1 direction from the rotating shaft 58, the annularelastic member 86 is even more greatly crush-pressed and deformedelastically by the elastic crush-pressing of the plate-like portion 125of the variable passage forming member 122 against the outer peripheralsurface 132 of the annular elastic member 86. Hence, the passagecross-sectional area of each communicating groove 121 is furthernarrowed by large embedment of the deforming portion of the annularelastic member 86 into the communicating groove 121, so that the passagecross-sectional area of the variable passage 123 is set to a very smallvalue by the crush-deformed annular elastic member 86, therebysubstantially minimizing the flow of the viscous fluid 3 in the chamber9 into the chamber 10 via the communicating hole 13 and substantiallystopping the above-described high-speed rotation through thepartitioning member 11. Hence, the rotation of the impact-absorbed bodywhich tends to rotate the rotating shaft 58 at high speed is stopped,thereby making it possible to positively hold the impact-absorbed body.

After the partitioning member 11 has been rotated in the R1 direction,as shown in FIG. 8, when the input of relative rotation in the R2direction from the rotating shaft 58 ceases, in the flow limiting means116, the partitioning member 11 begins to be conversely rotated in theR2 direction by the resiliency of the spiral spring 111. In thisrotation, the variable passage forming member 122 is relatively moved inthe R1 direction with respect to the partitioning member 11. As aresult, the embedment of the deforming portion of the annular elasticmember 86 with respect to the communicating grooves 121 is canceled, andthe annular passage 133 is reopened, thereby causing the flow of theviscous fluid 3 from the chamber 9 into the chamber 10 with smallresistance through such communicating grooves 121 and the annularpassage 133. Hence, the partitioning member 11 is speedily rotated inthe R2 direction with such a small resisting force, and the partitioningmember 11 is returned to its initial position.

As described above, when the internal pressure of the viscous fluid 3accommodated in the chamber 9 is generated in excess of a fixed value onthe basis of the rotation of the partitioning member 11 in the R1direction, the annular elastic member 86 is adapted to be elasticallydeformed by being brought into pressing contact with the end face 118 ofthe variable passage forming member 122 after the disappearance of theannular passage 133 on the basis of the relative movement of thevariable passage forming member 122, to thereby fill the communicatinggrooves 121 by its elastically deformed portions and reduce the passagecross-sectional area of the variable passage 123. Meanwhile, when theinternal pressure of the viscous fluid 3 accommodated in the chamber 10is generated in excess of a fixed value on the basis of the rotation ofthe partitioning member 11 in the R2 direction, the end face 118 of thevariable passage forming member 122 is adapted to relatively move awayfrom the annular elastic member 86 so as to form the annular passage133.

Also in this flow limiting means 116 adapted to brake the relativerotation in the R direction of the partitioning member 11 with respectto the vessel 4, the annular elastic member 86, which is made of naturalrubber or synthetic rubber having a small modulus of elasticity at hightemperature and a large modulus of elasticity at low temperature,undergoes large elastic deformation at high temperature and smallelastic deformation at low temperature in the crush-pressing by theplate-like portion 125. Therefore, coupled with the synergistic actionwith the viscous fluid 3 having a positive temperature characteristicconcerning fluidity whereby the fluidity increases at high temperatureand decreases at low temperature, it is possible to reduce thetemperature dependence of the flow resistance of the viscous fluid 3flowing through the variable passage 123 including the communicatinggrooves 121 whose passage cross-sectional area is determined by themagnitude of the elastic deformation of the annular elastic member 86.Thus, it is possible to reduce the difference, for instance, between, onthe one hand, the stiffness of the damper 1 in the R1 direction in thecase of an input of high-speed rotation exceeding a fixed value in whichcase the impact becomes large at high temperature and, on the otherhand, the stiffness of the damper 1 in the R1 direction in the case ofan input of high-speed rotation exceeding the fixed value in which casethe impact becomes large at low temperature. Hence, it becomes possibleto positively hold the impact-absorbed body with stiffness which doesnot differ so much both at high temperature and at low temperature withrespect to the R1 direction.

If the damper 1 having the flow limiting means 116 and the like isapplied to the above-described vehicle seat 201 shown FIGS. 11 and 12,the damper 1 operates in a similar manner.

The above-described damper 1 having the above-described flow limitingmeans 14 or the flow limiting means 116 is, in each case, adapted tobrake the relative rotation in the R direction of the partitioningmember 11 with respect to the vessel 4. Alternatively, however, thedamper may be adapted to brake the relative linear movement of thepartitioning member with respect to the vessel, as shown in FIGS. 20 and21.

Namely, the damper 1 shown in FIGS. 20 and 21 and having the flowlimiting means 14, for example, is comprised of a cylinder 152 servingas a vessel for accommodating the viscous fluid 3 in its interior 2; apiston 153 which is provided in the interior 2 of the cylinder 152linearly movably in the A direction, i.e., the axial direction, andwhich serves as a partitioning member for partitioning the interior 2 ofthe cylinder 152 for accommodating the viscous fluid 3 into the twochambers 9 and 10 in the A direction; the communicating hole 13 formedin the piston 153 so as to allow the two chambers 9 and 10 in theinterior 2 of the cylinder 152 to communicate with each other throughthe variable passage 12 whose passage cross-sectional area changes; anda resilient means 154 for resiliently urging the piston 153 in the A2direction with respect to the cylinder 152. When the internal pressureof the viscous fluid 3 accommodated in the chamber 9 in the A1direction, which is one direction in the A direction, is generated inexcess of a fixed value on the basis of the linear movement of thepiston 153 in the A1 direction, the flow limiting means 14 is adapted tolimit the flow of the viscous fluid 3 in the chamber 9 into the chamber10 in the A2 direction, which is the other direction in the A direction,through the communicating hole 13.

The cylinder 152 includes a hollow cylindrical body 163 integrallyhaving a small-diameter hollow cylindrical portion 161 and alarge-diameter hollow cylindrical portion 162; an annular bearing member164 fitted and secured to the inner peripheral surface of an open endportion of the small-diameter hollow cylindrical portion 161; an annularlid member 165 threadedly secured to the inner peripheral surface of theopen end portion of the small-diameter hollow cylindrical portion 161 bybeing located adjacent to the bearing member 164; and an annular closuremember 167 fitted and secured to an open end portion of thelarge-diameter hollow cylindrical portion 162 and having a mountingmember 166 formed integrally therewith. A seal ring 171 fitted to anannular groove 170 formed on an annular small-diameter outer peripheralsurface 168 of the closure member 167 is disposed between that outerperipheral surface 168 of the closure member 167 and a cylindrical innerperipheral surface 169 of the large-diameter hollow cylindrical portion162.

The piston 153 includes a bottomed hollow cylindrical base portion 176which is passed through the bearing member 164 and the lid member 165linearly movably in the A direction, and to which one end of a rod 175having a mounting member 174 at its other end disposed outside thecylinder 152 is secured; and an annular portion 178 which is formedintegrally on the outer peripheral surface of the base portion 176 andis, at its annular outer peripheral surface 177, in contact with theinner peripheral surface 169 of the large-diameter hollow cylindricalportion 162 linearly movably in the A direction. The annular portion 178is formed in the same way as the blade portion 47 or 48, and two flowlimiting means 14 are provided on such an annular portion 178.

Accordingly, each of the pair of flow limiting means 14 provided in theannular portion 178 includes the variable passage forming member 85which has the through hole 82 which, in the end face 81 in the A1direction, is open to the chamber 9 on the A1 direction side, thevariable passage forming member 85 being fitted to the annular portion178 movably in the A direction with respect to the annular portion 178in such a manner as to oppose at the end face 84 in the A2 direction theside face 75 of the annular portion 178, so as to form the variablepassage 12 communicating with, on the one side, the through hole 82 and,on the other side, the communicating hole 13 in cooperation with theside face 75 in the A1 direction of the annular portion 178; and theannular elastic member 86 surrounding the variable passage 12 anddisposed between the end face 84 in the A2 direction of the variablepassage forming member 85 and the side face 75 in the A1 direction ofthe annular portion 178.

The resilient means 154 has a coil spring 181 which has one end in the Adirection secured and connected to the bearing member 164 and the otherend in the A direction secured and connected to the annular portion 178and surrounds the rod 175. In the same way as the spiral spring 111, theresilient means 154 is adapted to linearly move the piston 153 in the A2direction by the resiliency of the coil spring 181 so as to return toits original position.

In the damper 1 shown in FIGS. 20 and 21, the above-described flowlimiting means 116 may be used in substitution of the flow limitingmeans 14. The flow limiting means 116 in this case includes the variablepassage forming member 122 which is movably fitted to the annularportion 178 and has, in its end face 118 facing the side face 75 of theannular portion 178, the communicating grooves 121 which arerespectively open at their one end portions 119 to the chamber 9 and areopen at their other end portions 120 to the communicating hole 13; andthe annular elastic member 86 which is located between the one endportion 119 and the other end portion 120 of each communicating groove121 in the radial direction and fitted to the side face 75 in the A1direction of the annular portion 178, such that the variable passage 123including the communicating grooves 121 for effecting mutualcommunication between the two chambers 9 and 10 in the vessel 2 by meansof the communicating hole 13 by allowing the chamber 9 and thecommunicating hole 13 to communicate is formed by the contact, pressingcontact, and non-contact of the annular elastic member 86 with respectto the end face 118 in the A2 direction of the variable passage formingmember 122 having the communicating grooves 121.

In the damper 1 shown in FIGS. 20 and 21 and having the flow limitingmeans 116, the variable passage forming member 122 includes theplate-like portion 125 having the communicating grooves 121; the pair ofleg portions 126 which have respective one end portions formedintegrally on the plate-like portion 125 and are inserted in thecommunicating hole 13; and the hook portions 127 which are respectivelyformed integrally on the other end portions of the pair of leg portions126 and prevent the leg portions 126 from coming off the communicatinghole 13. When the internal pressure of the viscous fluid 3 accommodatedin the chamber 10 on the A2 direction side is generated in excess of afixed value on the basis of the linear movement of the annular portion178 in the A2 direction, the end face 118 in the A2 direction of thevariable passage forming member 122 is adapted to move away from theannular elastic member 86. Meanwhile, when the internal pressure of theviscous fluid 3 accommodated in the chamber 9 on the A1 direction sideis generated in excess of a fixed value on the basis of the linearmovement of the annular portion 178 in the A1 direction, the annularelastic member 86 is adapted to be elastically deformed to thereby fillthe communicating grooves 121 and reduce the passage cross-sectionalarea of the variable passage 12.

The damper 1 shown in FIGS. 20 and 21 can also be used in the vehicleseat 201, as shown in FIGS. 22 and 23. In this case, the damper 1 whichis extended and contracted in the A direction by the relative linearmovement in the A direction of the cylinder 152 with respect to thepiston 153 is used in the vehicle seat 201 by being provided midway inthe wire 228 by means of the mounting members 166 and 174. The rotatingshaft 58 is secured to the arm member 227 and is directly supportedtogether with the supporting shaft 226 rotatably in the R1 and R2directions.

The vehicle seat 201 equipped with the damper 1 shown in FIGS. 20 and 21also has the transmitting mechanism 223 equipped with the damper 1serving as a switching mechanism whereby the force applied to thebackrest 204 in the backward direction of the vehicle at a velocityexceeding a fixed value is transmitted to the inhibition mechanism 207so as to cancel the inhibition by the inhibition mechanism 207 of therotation of the headrest 205 in the forward R3 direction, whereas theforce applied to the backrest 204 at a velocity of the fixed value orless is not transmitted to the inhibition mechanism 207 so as tomaintain the inhibition by the inhibition mechanism 207 of the rotationof the headrest 205 in the forward R3 direction. Therefore, it ispossible to positively move the headrest 205 in the forward R3 directiononly at the time of such as a collision by properly discriminating thetime of such as a collision and the time of a non-collision.

1. A damper comprising: a vessel for accommodating a viscous fluid inits interior; at least one hampering wall provided in the interior ofsaid vessel to hamper the flow of the viscous fluid in a direction aboutan axis of said vessel; a partitioning member for partitioning theinterior of said vessel accommodating the viscous fluid whose flow hasbeen hampered by said hampering wall into at least two chambers in thedirection about the axis, said partitioning member being provided in theinterior of said vessel rotatably in the direction about the axis withrespect to said vessel; at least one communicating hole formed in saidpartitioning member so as to allow the two chambers in the interior ofsaid vessel to communicate with each other via a variable passage whosepassage cross-sectional area changes; and flow limiting means forlimiting the flow of the viscous fluid in the chamber on one directionside in the direction about the axis into the chamber on anotherdirection side in the direction about the axis through saidcommunicating hole when the internal pressure of the viscous fluidaccommodated in the chamber on the one direction side in the directionabout the axis has exceeded a fixed value on the basis of the rotationof said partitioning member in the one direction in the direction aboutthe axis with respect to said vessel, wherein said flow limiting meansincludes: a variable passage forming member which has a through holewhich, in an end face in the one direction in the direction about theaxis of said variable passage forming member, is open to the chamber onthe one direction side in the direction about the axis, said variablepassage forming member being fitted to said partitioning member movablyin such a manner as to oppose, at an end face in another direction inthe direction about the axis of said variable passage forming member, aside face in the one direction in the direction about the axis of saidpartitioning member, so as to form the variable passage communicatingwith, on one side, the through hole and, on another side, saidcommunicating hole in cooperation with the side face in the onedirection in the direction about the axis of said partitioning member;and an annular elastic member surrounding the variable passage anddisposed between the end face in the other direction in the directionabout the axis of the said variable passage forming member and the sideface in the one direction in the direction about the axis of saidpartitioning member, so as to brake the relative rotation in thedirection about the axis of said partitioning member with respect tosaid vessel.
 2. The damper according to claim 1, wherein said variablepassage forming member has a plate-like portion having the through hole,a leg portion formed, at its one end portion, integrally on theplate-like portion and inserted in said communicating hole, and a hookportion formed integrally on another end portion of the leg portion soas to prevent the leg portion from coming off said communicating hole.3. The damper according to claim 1 or 2, wherein said partitioningmember has a truncated conical surface in the side face in the onedirection in the direction about the axis, said variable passage formingmember has a truncated conical surface which is complementary to thetruncated conical surface of said partitioning member and opposes thattruncated conical surface, and the variable passage has a truncatedconical passage formed by the truncated conical surface of saidpartitioning member and the truncated conical surface of said variablepassage forming member.
 4. A damper comprising: a vessel foraccommodating a viscous fluid in its interior; at least one hamperingwall provided in the interior of said vessel to hamper the flow of theviscous fluid in a direction about an axis of said vessel; apartitioning member for partitioning the interior of said vesselaccommodating the viscous fluid whose flow has been hampered by saidhampering wall into at least two chambers in the direction about theaxis, said partitioning member being provided in the interior of saidvessel rotatably in the direction about the axis with respect to saidvessel; at least one communicating hole formed in said partitioningmember so as to allow the two chambers in the interior of said vessel tocommunicate with each other via a variable passage whose passagecross-sectional area changes; and flow limiting means for limiting theflow of the viscous fluid in the chamber on one direction side in thedirection about the axis into the chamber on another direction side inthe direction about the axis through said communicating hole when theinternal pressure of the viscous fluid accommodated in the chamber onthe one direction side in the direction about the axis has exceeded afixed value on the basis of the rotation of said partitioning member inthe one direction in the direction about the axis with respect to saidvessel, wherein said flow limiting means includes: a variable passageforming member which is movably fitted to said partitioning member andhas, in its end face in the other direction in the direction about theaxis facing a side face in the one direction in the direction about theaxis of said partitioning member, a communicating groove which is openat its one end portion to said chamber on the one direction side in thedirection about the axis and is open at its other end portion to saidcommunicating hole; and an annular elastic member which is locatedbetween the one end portion and the other end portion of thecommunicating groove in a radial direction and fitted to the side facein the one direction in the direction about the axis of saidpartitioning member, such that the variable passage for effecting mutualcommunication between the two chambers in said vessel by means of saidcommunicating hole by allowing said chamber on the one direction side inthe direction about the axis and said communicating hole to communicateis formed by the contact, pressing contact, and non-contact of saidannular elastic member with respect to the end face in the otherdirection in the direction about the axis of said variable passageforming member having the communicating groove, so as to brake therelative rotation in the direction about the axis of said partitioningmember with respect to said vessel.
 5. The damper according to claim 4,wherein said variable passage forming member has a plate-like portionhaving the communicating groove, a leg portion formed, at its one endportion, integrally on the plate-like portion and inserted in saidcommunicating hole, and a hook portion formed integrally on another endportion of the leg portion so as to prevent the leg portion from comingoff said communicating hole.
 6. The damper according to claim 4 or 5,wherein when the internal pressure of the viscous fluid accommodated insaid chamber in the other direction in the direction about the axis isgenerated in excess of a fixed value on the basis of the rotation ofsaid partitioning member in the other direction in the direction aboutthe axis with respect to said vessel, the end face in the otherdirection in the direction about the axis of said variable passageforming member is adapted to move away from said annular elastic member.7. The damper according to any one of claims 4 to 6, wherein when theinternal pressure of the viscous fluid accommodated in said chamber onthe one direction side in the direction about the axis is generated inexcess of a fixed value on the basis of the rotation of saidpartitioning member in the one direction in the direction about the axiswith respect to said vessel, said annular elastic member is adapted tobe elastically deformed to fill the communicating groove and reduce thepassage cross-sectional area of the variable passage.
 8. The damperaccording to any one of claims 1 to 7, further comprising resilientmeans for resiliently urging said partitioning member in the otherdirection in the direction about the axis with respect to said vessel.9. A damper comprising: a vessel for accommodating a viscous fluid inits interior; a partitioning member provided in the interior of saidvessel linearly movably in an axial direction with respect to saidvessel to partition the interior of said vessel for accommodating theviscous fluid into at least two chambers in the axial direction; atleast one communicating hole formed in said partitioning member so as toallow the two chambers in the interior of said vessel to communicatewith each other through a variable passage whose passage cross-sectionalarea changes; flow limiting means for limiting the flow of the viscousfluid in the chamber on one direction side in the axial direction intothe chamber on another direction side in the axial direction throughsaid communicating hole when the internal pressure of the viscous fluidaccommodated in the chamber on the one direction side in the axialdirection has exceeded a fixed value on the basis of the linear movementof said partitioning member in one direction in the axial direction withrespect to said vessel, wherein said flow limiting means includes: avariable passage forming member which has a through hole which, in anend face in the one direction in the axial direction of said variablepassage forming member, is open to the chamber on the one direction sidein the direction about the axis, said variable passage forming memberbeing fitted to said partitioning member linearly movably in such amanner as to oppose, at an end face in another direction in the axialdirection of said variable passage forming member, a side face in theone direction in the axial direction of said partitioning member, so asto form the variable passage communicating with, on one side, thethrough hole and, on another side, said communicating hole incooperation with the side face in the one direction in the axialdirection of said partitioning member; and an annular elastic membersurrounding the variable passage and disposed between the end face inthe other direction in the axial direction of the said variable passageforming member and the side face in the one direction in the axialdirection of said partitioning member, so as to brake the relativelinear movement in the axial direction of said partitioning member withrespect to said vessel.
 10. The damper according to claim 9, whereinsaid variable passage forming member has a plate-like portion having thethrough hole, a leg portion formed, at its one end portion, integrallyon the plate-like portion and inserted in said communicating hole, and ahook portion formed integrally on another end portion of the leg portionso as to prevent the leg portion from coming off said communicatinghole.
 11. The damper according to claim 9 or 10, wherein saidpartitioning member has a truncated conical surface in the side face inthe one direction in the axial direction, said variable passage formingmember has a truncated conical surface which is complementary to thetruncated conical surface of said partitioning member and opposes thattruncated conical surface, and the variable passage has a truncatedconical passage formed by the truncated conical surface of saidpartitioning member and the truncated conical surface of said variablepassage forming member.
 12. A damper comprising: a vessel foraccommodating a viscous fluid in its interior; a partitioning memberprovided in the interior of said vessel linearly movably in an axialdirection with respect to said vessel to partition the interior of saidvessel for accommodating the viscous fluid into at least two chambers inthe axial direction; at least one communicating hole formed in saidpartitioning member so as to allow the two chambers in the interior ofsaid vessel to communicate with each other through a variable passagewhose passage cross-sectional area changes; flow limiting means forlimiting the flow of the viscous fluid in the chamber on one directionside in the axial direction into the chamber on another direction sidein the axial direction through said communicating hole when the internalpressure of the viscous fluid accommodated in the chamber on the onedirection side in the axial direction has exceeded a fixed value on thebasis of the linear movement of said partitioning member in onedirection in the axial direction with respect to said vessel, whereinsaid flow limiting means includes: a variable passage forming memberwhich is movably fitted to said partitioning member and has, in its endface in another direction in the axial direction facing a side face inthe one direction in the axial direction of said partitioning member, acommunicating groove which is open at its one end portion to saidchamber on the one direction side in the axial direction and is open atits other end portion to said communicating hole; and an annular elasticmember which is located between the one end portion and the other endportion of the communicating groove in a radial direction and fitted tothe side face in the one direction in the axial direction of saidpartitioning member, such that the variable passage for effecting mutualcommunication between the two chambers in the interior of said vessel bymeans of said communicating hole by allowing said chamber on the onedirection side in the axial direction and said communicating hole tocommunicate is formed by the contact, pressing contact, and non-contactof said annular elastic member with respect to the end face in the otherdirection in the axial direction of said variable passage forming memberhaving the communicating groove, so as to brake the relative linearmovement in the axial direction of said partitioning member with respectto said vessel.
 13. The damper according to claim 12, wherein saidvariable passage forming member has a plate-like portion having thecommunicating groove, a leg portion formed, at its one end portion,integrally on the plate-like portion and inserted in said communicatinghole, and a hook portion formed integrally on another end portion of theleg portion so as to prevent the leg portion from coming off saidcommunicating hole.
 14. The damper according to claim 12 or 13, whereinwhen the internal pressure of the viscous fluid accommodated in saidchamber in the other direction in the axial direction is generated inexcess of a fixed value on the basis of the linear movement of saidpartitioning member in the other direction in the axial direction withrespect to said vessel, the end face in the other direction in the axialdirection of said variable passage forming member is adapted to moveaway from said annular elastic member.
 15. The damper according to anyone of claims 12 to 14, wherein when the internal pressure of theviscous fluid accommodated in said chamber on the one direction side inthe axial direction is generated in excess of a fixed value on the basisof the linear movement of said partitioning member in the one directionin the axial direction with respect to said vessel, said annular elasticmember is adapted to be elastically deformed to fill the communicatinggroove and reduce the passage cross-sectional area of the variablepassage.
 16. The damper according to any one of claims 9 to 15, furthercomprising resilient means for resiliently urging said partitioningmember in the other direction in the axial direction with respect tosaid vessel.
 17. The damper according to any one of claims 1 to 16,wherein said annular elastic member is constituted by an O-ring formedof natural rubber or synthetic rubber whose modulus of elasticity issmall at a high temperature and large at a low temperature.
 18. Avehicle seat comprising: a backrest of a vehicle; a headrest supportedby said backrest movably in a forward direction of the vehicle; movementurging means for urging said headrest to move in the forward direction;an inhibition mechanism for inhibiting the movement of said headrest inthe forward direction; and canceling means for canceling the inhibitionby said inhibition mechanism of the movement of said headrest in theforward direction when a moving velocity of a force applied to saidbackrest in a backward direction of the vehicle has exceeded a fixedvalue, said canceling means having a load-rotation converting mechanismfor converting a load applied to a back receiving portion of saidbackrest into a rotational force and a transmitting mechanism fortransmitting to said inhibition mechanism a force applied to saidbackrest in the backward direction of the vehicle on the basis of themoving velocity exceeding the fixed value, said transmitting mechanismhaving said damper according to any one of claims 1 to 15, wherein oneof said vessel and said partitioning member of said damper is coupled tosaid load-rotation converting mechanism, and another one of said vesseland said partitioning member of said damper is coupled to saidinhibition mechanism.
 19. The vehicle seat according to claim 18,wherein said load-rotation converting mechanism has a load receivingplate supported rotatably by a frame of said backrest and disposed inthe back receiving portion of said backrest.
 20. The vehicle seataccording to claim 18 or 19, wherein said headrest is supported by saidbackrest rotatably or linearly movably in the forward direction, saidmovement urging means is adapted to urge said headrest to rotate orlinearly move in the forward direction, and said inhibition mechanism isadapted to inhibit the rotation or linear movement of said headrest inthe forward direction.